1. Field of the Invention
The present invention relates to a field emission type display capable of displaying multiple gradations.
2. Description of the Related Art
A field emission type display comprises emitter electrodes connected to cathode lines, gate electrodes and anode electrodes. A fluorescent substance is coated on the anode electrodes. The emitter electrode emits electrons corresponding to an electric field between the gate electrode and the emitter electrode. A high potential difference is applied between the emitter electrode and the anode electrode. The high potential difference accelerates the electrons emitted from the emitter electrode in the direction of the anode electrode. The electrons reaching the anode electrode cause the fluorescent substance to glow, thus making a luminescent spot per pixel. Accordingly, the quantity of luminescence of the fluorescent substance may be controlled by the quantity of electrons emitted from the emitter electrode.
An areal gradation method for a liquid crystal display has been proposed in Japanese Patent Laid-Open No. Hei. 4-242223. An intersection of a scan line electrode and a signal line electrode corresponds to a pixel here because it is a liquid crystal display. When an electric field is produced between the scan line electrode and the signal line electrode, a liquid crystal layer sandwiched by both electrodes becomes transparent or opaque.
In the document described above, signal lines, each having a different line width, are provided within one pixel so as to function as if one pixel is divided corresponding to the width of the signal line. Five signal lines P1, P2, P3, P4 and P5 are provided within one pixel as shown in FIG. 16, which shows a conventional liquid crystal display. Here, the respective signal lines have the width ratio of 1, xc2xd, xc2xd, xc2xc and xc2xc. Further, a signal line P3 has a width of xc2xd and is covered by a filter provided with a window P6 having one half of the area of a signal line P2. A signal line P4 has a width of xc2xc and is covered by a filter having a window P7 having the same height as the signal line P3. A signal line P5 has a width of xc2xc and is covered by a filter provided with a window P8 having one half of the area of the signal line P4. Thereby, display areas corresponding to the gradations of 1, xc2xd, xc2xc, xe2x85x9 and {fraction (1/16)} may be created.
While signal lines having different line widths are provided within one pixel in this method, the width of the cathode line electrode for reproducing the first gradation must be very thin as compared to the width of one pixel in order to represent 256 gradations. For instance, the width is set at {fraction (1/16)} of the width of the pixel and the window is set at {fraction (1/16)}. When the line width is calculated in trial without any window as a quick estimation, and when the size of the pixel is set at 150 xcexcm (vertical)xc3x97450 xcexcm (horizontal) and the pitch between the cathode lines is set at 10 xcexcm, the least width of the cathode line turns out to be 0.27 xcexcm which is difficult to fabricate. Further, the wiring cannot be formed uniformly because the width of the cathode line differs; therefore, the image quality may deteriorate due to stepwise cuts (phenomenon in which the wire is cut in the current path) and to the increase of wiring resistance. It also becomes difficult to contact the cathode lines with the cathode line driving circuit, thus causing a failure.
Accordingly, while the areal gradation method has been proposed for the conventional field emission type display, the wiring cannot be uniform because the width of the cathode line is different and the image quality deteriorates due to the stepwise cuts and to the increase of wiring resistance. It is also difficult to contact the cathode lines with the cathode line driving circuit as described above.
Accordingly, an object of the present invention is to provide a field emission type display which is capable of suppressing the deterioration of the image quality which otherwise occurs due to the stepwise cuts and to the increase of the wiring resistance caused by the width of the cathode line and which causes less failures by improving the conduction between an emitter electrode and the cathode line.
The inventive display provides pixels disposed on a display substrate in a matrix in X and Y directions. A plurality of field emission type emitters is provided within one pixel and gate electrodes for switching the field emission type are provided, respectively. An opposed substrate having an anode electrode and fluorescent substance is disposed so as to face the display substrate.
The display also comprises a plurality of cathode lines disposed in the column direction to drive the field emission type emitters and gate lines for driving the pixels in the row direction in common.
The display also comprises a gate line driving circuit for supplying voltage to the gate lines, a cathode line driving circuit for supplying voltage to the cathode lines and an anode electrode driving circuit for supplying voltage to the anode electrode.
The invention display has the line width of the cathode lines within one pixel the same and implements the areal gradation representing scheme by differentiating the area of the emitters emitting light within one pixel.
Besides the lines with equal width, lines having a width dispersion of around 10% are also considered to be the same in the cathode line width described above, because the effect of the present invention may be fully obtained even if the line width differs by around 10%. This includes slight modification of the line width in the designing step besides the dispersion of products caused during manufacturing.
The specific nature of the present invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawings.
The present invention is directed to a field emission display comprising an anode; a fluorescent layer on said anode; a board spaced apart from said anode; a plurality of cathode lines parallel to each other on said board; an insulating layer on said cathode lines; a gate electrode on said insulating layer, and said gate electrodes disposed above and may be substantially perpendicular to said cathode lines; and emitter elements connected to said cathode lines, and said emitter elements exposed from openings on said gate electrode and said insulating layer, wherein a cross point of said plurality of cathode lines and said gate electrode forms a pixel, numbers of said emitter elements connected to each cathode line are different in said pixel.
The present invention introduces a field emission display comprising an anode; a fluorescent layer on said anode; a board spaced apart from said anode; a plurality of cathode lines parallel to each other on said board; a first insulating layer having through holes and disposed on said cathode lines; emitter electrodes on said first insulating layer, and each of said emitter electrode connected to one of said cathode lines via a contact in a respective one of said through holes; a second insulating layer; a gate electrode on said second insulating layer, and said gate electrodes disposed above and may be substantially perpendicular to said cathode lines; and emitter elements formed on said emitter electrodes, and said emitter elements exposed from openings on said gate electrode and said second insulating layer, wherein a cross point of said plurality of cathode lines and said gate electrode forms a pixel, numbers of said emitter elements connected to each cathode line are different in said pixel.
The present invention further introduces a driving method for a field emission display comprising impressing a pulse selected from pulses having different duty ratios to at least one of said cathode lines corresponding to an image signal for said pixel.